[Webtoon study] Add genre-specific episode ending builder and QA checks

[realproject7]

Context

The sample endings are not generic conclusions. They close by sharpening the genre promise: a modern-fantasy reward loop, thriller dread, romance complication, or slice-of-life gag. OWS should help agents and users design an ending turn explicitly.

Required Changes

Add ending-turn support to cartoon planning and QA:

• Ending type selector: loop, cliffhanger, dread image, relationship reversal, gag close, mystery clue, power consequence, social consequence.
• Required fields: readerQuestionAfterEpisode, nextEpisodePressure, lastVisualFunction, lastLineFunction.
• Agent prompt section that proposes 2-3 possible ending turns before choosing one.
• QA warnings when the final sequence ends without a clear turn.

Acceptance Criteria

• Episode metadata records ending type and next-reader question.
• Progress/preview can show the ending goal without taking over the editor UI.
• Agents can revise endings without rewriting the whole episode.
• QA catches missing/weak ending turn in cartoon episodes.

Verification

• Unit tests for ending-turn defaults and QA rules.
• Create original genre test episodes with four different ending types.
• Confirm publish preview includes the intended final sequence.